This invention relates to olefin polymerization catalysts.
Aluminum phosphate alone or with various other metals is known as a hydrocarbon conversion catalyst. Aluminum phosphate is also known as a base for chromium in olefin polymerization reactions. With chromium on silica olefin polymerization catalysts, it has been found that a more economical route to olefin polymerization is to utilize a slurry system for the polymerization. This, however, produces relatively low melt flow polymer because it is not feasible to raise the temperature in order to increase the melt flow as is the case in solution systems. Thus, much technology has developed on methods to raise the melt flow in catalyst systems utilizing chromium on silica. Recently, it has been discovered that chromium on aluminum phosphate can be utilized to produce olefin polymers having high melt flow. Here again, with the slurry system, there is very little leeway in controlling melt flow through temperature control. Consequently, chromium on aluminum phosphate may result in the production of polymer which has a greater melt flow than is desired and this cannot be reduced as a practical matter by reducing the temperature. Thus, there is a need for increasing the flexibility of molecular weight control in chromium on aluminum phosphate catalyst systems.